The basic objectives of the proposed research are to study renal tubular function by in vitro microperfusion techniques. During the forthcoming fiscal year the specific areas which we wish to examine are: 1) Continue the characterization of the transport properties of the two functionally different populations of proximal tubules. 2) Describe the anatomical characteristics of the thin descending and ascending limbs by electron microscopic techniques. 3) Study the differences between functions of the distal convoluted tubule as contrasted to the cortical collecting duct. Specific emphasis will be placed on interdependence of diuretic and aldosterone effects. 4) Study the effect of prostaglandins on salt and water transport in thick ascending limb of Henle, distal convoluted tubule and cortical collecting duct.